Updated: Jul 2
Not all microbes are created equal. Each phylum, class, family, genus, species, strain and cell is imparted with a particular genetic potential. This unique array of genetic information manifests as a metabolic arsenal. Some microbes use this metabolic potential to enhance the development of a host organism–these are probiotics. Other microbes refine their abilities so as to destructively extract resources from other organisms–these are pathogens. The line between probiotic and pathogen can be blurred amongst the chaotic fog of ecology. But for the reef aquarist, horticulturist, oysterman and shrimp farmer alike, what is clear is that the microbe which destroys the crop is the enemy–and the microbe which is the enemy of that enemy… is a friend. It cannot be overstated that not all microbes are created equal: Some are slackers. Some are salarymen. Some are opportunists Some are violent conquers The Vibrionaceae contains a multitude of microbes which can be described as both opportunists and conquerors. V. cholerae is a classic example of a devastating human pathogen, but members of this genus are capable of destabilizing the gastrointestinal systems of chickens, swine and bovines. V. anguillarum is a devastating fish pathogen which infects commercial salmonid species like rainbow trout (Onchyronous mykiss) and Atlantic salmon (Salmo salar). Certain Vibrio species specialize in the infection of seahorses. Species like V. coralliilyticus and V. tubiashii acutely kill the larvae/juveniles of valuable commercial shellfish species such as the Eastern and Pacific oyster (Crassostrea virginica/gigas). V. tapetis causes ‘brown-ring disease’ in many commercial clam (Mercenaria) species. V. vulnificus accumulates in the tissues of such shellfish, inducing food poisoning in the humans which consume them. V. proteolyticus has been known to devastate brine shrimp (Artemia salina) ponds. V. alginolyticus and V. harveyi are responsible for tremendous loss in both the
hatchery of tiger prawns (Penaeus monodon) and Pacific white legged shrimp (Litopaneus vannamei). V. parahaemolyticus can be responsible for hepatopancreatic necrosis disease and the resulting devastating loss in commercial shrimp grow-out ponds/tanks. In this disease, infectious V. parahaemolyticus colonizes the shrimp’s all-important hepatopancreas organ and ‘digests’ it through a variety of molecular weaponry (alkaline proteases, metalloproteases, cysteine proteases, alkaline serine proteases, etc.). Without effective protection or remedy, such attacks of vibriosis can be incredibly devastating to shrimp crops and financially compromise farmers overnight.
Vibrio spp. pathogens are responsible for devastating coral loss both in the aquarium and on wild reefs. The pathogenicity of V. shiloi in the coral Oculina patagonica has been well described. V. shiloi normally exists in a planktonic form at relatively sparse atmospheric levels. V. shiloi can attack to the surfaces of Oculina patagonica and other coral, but adherence success is directly dictated by the activity of the Symbiodinium sp. and other coral symbionts. If conditions occur, such as unfavorable warm temperatures, the coral symbionts are less effective and more V. shiloi cells can successfully adhere to the coral surface. After a critical infection threshold is achieved, adhered Vibrio cells can grow and infect the gastrodermal tissue of the coral. This is the tissue which holds the host of the coral’s photosynthetic symbionts. The resulting vibriosis kills the coral in two ways. Firstly, it results in the continual expulsion of coral symbionts or coral bleaching. Secondly, a successful Vibrio infection releases toxins to directly destroy host tissue. Similar occurrences of vibriosis can manifest as diseases such as ‘yellow-band’ or ‘white-band’ disease in various Caribbean and Indo-Pacific stony coral species. The difficult part to confronting the threat of vibriosis is accepting that Vibrio naturally occurs in nearly all ‘healthy’ systems. It is not merely a question of eradication as Vibrio is nearly ubiquitous in all aquatic and terrestrial ecosystems and functionally participates in those ecologies. Vibrio behavior is nuanced, highly-context driven and difficult to generalize. There is an imperative need to predict the factors which trigger ‘virulency,’ or the behaviors which manifest disease. Most of the time, virulency is not expressed as Vibrio cells live in relative benign relation to the fish/shellfish/shrimp around them.
Sometimes this relationship can even be beneficial, as planktonic V. fischeri are known to colonize the organs of deep sea fish. The Vibrio then produces bioluminescent compounds to the host’s benefit. The operative difference between relatively independent-planktonic V. fischeri cells and the highly organized, symbiotic cells lighting up marine hatchet fish is the presence of quorums. Quorums are signaling molecules produced by microbes to ‘communicate’ between cells. A certain operational level of quorum signaling must be established in order to manifest successful symbiosis…and/or disease. Quorums are how Vibrio spp. and other microbes communicate within their own species, as well as with others. Most Vibrio-animal/plant interactions (at least those focused on by humans) are of a negative nature. Various forms of vibriosis have the ability to devastate numerous terrestrial and aquatic crops, making it an imperative to understand which factors contribute to virulence and to identify beneficial microbes which can counter Vibrio aggregation before disease manifests. After all, not all microbes are created equal: Some are slackers. Some are salarymen. Some are Invaders Some are Patriots Hydrospace LLC has been enthusiastically researching and developing various probiotic strains to act as microbial soldiers in the war against vibriosis. The purple non-sulfur bacteria (Rhodopseudomonas, Rhodospirillum, Rhodobacter, etc.) have naturally evolved various metabolic abilities which allow them to compete with Vibrio for space, starve them of resources, disrupt their communications and kill them outright.
PNSB fortify host immunity
A good defense is also a good deterrent. Many if not all mass vibriosis outbreaks are the result of conditions which suppressed the natural immunity of the host species. In commercial aquaculture, this could be overfeeding resulting in decreased oxygen and elevated ammonia, nitrite, phosphate, CO2 or sulfide levels. Any of these conditions could induce stress and suppress the immunity of the fish/shellfish/coral crop. For example, Pocillopora damicornis colonies will predictably contract Vibrio infections only at
temperatures above 27.5 °C. Other water quality parameters, such as build-up of excess suspended organics, accelerate the growth of Vibrio cells, creating a perfect storm for virulency to occur. On the contrary, if environmental conditions are ideal, then most organisms have a tremendous capacity to dispatch small-scale Vibrio invasions. PNSB stimulate and enhance this natural immunity. Koga et al 2022 associated increased immune competence in kuruma prawns (Marsupenaeus japonicus) colonized with the PNSB Rhodovulum sulfidophilum. Alloul et al 2020 demonstrated in a feeding trial that Pacific white shrimp (Litopaneus vannamei) had a survival of 8% when fed a commercial diet during an ammonia stress trial (3 ppm), whilst shrimp which were fed a diet enriched with active Rhodopseudomonas palustris experienced a survival rate of 63-75%! One principle in farming holds that organisms raised in a ‘sterile bubble’ are extremely fragile to every contamination, whereas organisms associated with a diverse beneficial microbiome are always being exposed to bacterial components (bacterial lipopolysaccharides, peptidoglycans, glucans, phenol oxidases, etc.) without ever being subject to genuine infection. This process works the same as vaccination in that it raises the general immune alertness of the host, but is in many ways far superior. For example, the host's immunity evolves and adapts as the microbes around it do.
PNSB starves Vibrio into submission
Farming is largely not a practice of conservancy, and organisms must often be produced at high densities in the name of economic feasibility. The excess wastes associated with intensive production are likely to rapidly increase Vibrio concentrations, increasing the likelihood of virulency. It is therefore vital that waste metabolites (e.g., ammonia, nitrite, sulfides, organic sludge) be intercepted by powerful biofiltration agents such as PNSB. Species such as Rhodopseudomonas palustris, possess ‘swiss-army knife’ metabolisms, allowing them to switch between any of many beneficial biochemical reactions (photosynthesis, nitrification, denitrification, heterotrophy, etc.) under a WIDE array of environmental conditions. This allows PNSB to carry the resource war to any front.
Vibrio is willing to occupy. When outcompeted for resources, Vibrio is unlikely to achieve the densities needed for virulency. Furthermore, PNSB competes with Vibrio for space itself by forming biofilms on surfaces and rapidly populating turbid water, denying Vibrio any sizable territory on which to establish itself.
PNSB disrupts Vibrio communication
As stated above, signaling molecules (i.e., quorums) are essential for Vibrio cells to conduct collective behaviors such as biofilm formation or to manifest disease. Certain organisms have the ability to ‘quench’ the signaling of other species. Certain species of PNSB, such as Rhodospirillum rubrum, have been demonstrated to have this ‘quorum quenching’ ability, and therefore can significantly disrupt the communication between Vibrio cells!
PNSB destroy Vibrio
PNSB also have the ability to produce antibiotic compounds, such as streptomycin, which directly neutralize Vibrio cells. Alloul et al 2021 demonstrated that the purple-non sulfur bacteria Rhodopseudomonas palustris, Rhodobacter. capsulatus, Rhodobacter sphaeroides and Rhodospirillum rubrum suppressed V. parahaemolyticus and V. campbellii in agar plate trials. Many species of PNSB are currently being investigated for specific antibacterial and antiviral products to explain how they so often are able to dominate organically-rich ecosystems.
Vibriosis is an unavoidable challenge to the aquatic and the terrestrial cultivator alike. If unobserved and uncontrolled, various Vibrio spp. strains have the potential to unleash deadly chaos upon a whole range of market species, be they cows, chickens, pigs, staghorn corals, penaeid shrimps, Artemia, clams or oysters. Identifying the risk factors which drive Vibrio virulence is key, but so too is establishing a powerful microbial community to actively suppress outbreaks. Due to their incredible array of biochemical tools, PNSB (Rhodopsudomonas, Rhodobacter, Rhodospirillum) are able to sustain a favorable environment for animals/plants while constantly stimulating/fortifying their natural immunity. At the same time, a robust PNSB biofilter constantly competes with Vibrio cells for resources, creates biofilms to prevent their settlement, disrupts their inter-cell communications and kills them outright with chemical weaponry. Coral farmers, shellfish farmers, chicken farmers, pig farmers and shrimp farmers alike all deserve a powerful ally in the war against vibriosis. After all, it cannot be overstated that not all microbes are created equal: Some are there for the good times Some pack their bags and run Some microbes induce terrible sickness Some microbes fight to right what is wrong
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